The intensity of water-saving irrigation determines yield and soil carbon co-benefits in paddy rice

Context or problem Water scarcity and climate change have promoted water-saving irrigation (WSI) as a key strategy for sustainable rice production, yet the intensity of water deficit critically determines whether WSI practices achieve synergistic gains among yield, soil carbon sequestration, and microbial functionality. Objectives This study aimed to elucidate how different intensities of water deficit affect rice yield, soil carbon pools, and microbial diversity, and to determine how early- and late-season rice cultivation practices modulate these responses, thereby informing spatiotemporally adaptive irrigation strategies and season-specific rice management. Methods A global meta-analysis integrated 494 datasets from 92 independent experiments, assessing the responses of yield, soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), Shannon diversity, and Chao1 richness to WSI practices. Subgroup analyses evaluated varietal and seasonal responses. Results Results revealed that, compared with conventional flooding, WSI practices increased rice yield by 2.65%, MBC by 14.94%, and the Shannon index by 2.24%. In contrast, the overall SOC response was small and not statistically significant, with SOC increasing by only 0.22% (95% CI: −1.77–2.26%). These responses varied across WSI intensities. Mild alternate wetting and drying (AWD) irrigation had a synergistic effect on yield increase, carbon sequestration, and microbial community diversity, with yield, soil organic carbon, and Shannon index increasing by 5.88%, 5.99%, and 3.06%, respectively. Yield responses were also higher in indica rice than in japonica rice, increasing by 4.98% and 3.30%, respectively, and were stronger in early-season rice than in late-season rice, increasing by 4.95% and 2.78%, respectively. Owing to high heterogeneity, positive effects of WSI are restricted to mild deficit intensities, whereas stronger water deficits do not consistently enhance crop or soil responses. Conclusion This meta-analysis demonstrates that mild WSI balances rice productivity and ecological sustainability through spatiotemporally adaptive mechanisms, unveiling a dynamic “yield-carbon-microbe” nexus where optimized WSI orchestrates synergistic gains in yield, soil carbon, and microbial functionality. Differences in intensity-response patterns between early- and late-season rice highlight the importance of considering season-specific contexts in water management. Implications or significance Ultimately, this study provides a scientific basis for the development of precision irrigation management and offers practical guidance for sustainable rice production management.